available option letters are
    shown in <xref linkend="posix-embedded-options-table"/>.
    Note that these same option letters are used in the <replaceable>flags</replaceable>
    parameters of regex functions.
   </para>

   <table id="posix-embedded-options-table">
    <title>ARE Embedded-Option Letters</title>

    <tgroup cols="2">
     <thead>
      <row>
       <entry>Option</entry>
       <entry>Description</entry>
      </row>
     </thead>

      <tbody>
       <row>
       <entry> <literal>b</literal> </entry>
       <entry> rest of RE is a BRE </entry>
       </row>

       <row>
       <entry> <literal>c</literal> </entry>
       <entry> case-sensitive matching (overrides operator type) </entry>
       </row>

       <row>
       <entry> <literal>e</literal> </entry>
       <entry> rest of RE is an ERE </entry>
       </row>

       <row>
       <entry> <literal>i</literal> </entry>
       <entry> case-insensitive matching (see
       <xref linkend="posix-matching-rules"/>) (overrides operator type) </entry>
       </row>

       <row>
       <entry> <literal>m</literal> </entry>
       <entry> historical synonym for <literal>n</literal> </entry>
       </row>

       <row>
       <entry> <literal>n</literal> </entry>
       <entry> newline-sensitive matching (see
       <xref linkend="posix-matching-rules"/>) </entry>
       </row>

       <row>
       <entry> <literal>p</literal> </entry>
       <entry> partial newline-sensitive matching (see
       <xref linkend="posix-matching-rules"/>) </entry>
       </row>

       <row>
       <entry> <literal>q</literal> </entry>
       <entry> rest of RE is a literal (<quote>quoted</quote>) string, all ordinary
       characters </entry>
       </row>

       <row>
       <entry> <literal>s</literal> </entry>
       <entry> non-newline-sensitive matching (default) </entry>
       </row>

       <row>
       <entry> <literal>t</literal> </entry>
       <entry> tight syntax (default; see below) </entry>
       </row>

       <row>
       <entry> <literal>w</literal> </entry>
       <entry> inverse partial newline-sensitive (<quote>weird</quote>) matching
       (see <xref linkend="posix-matching-rules"/>) </entry>
       </row>

       <row>
       <entry> <literal>x</literal> </entry>
       <entry> expanded syntax (see below) </entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   <para>
    Embedded options take effect at the <literal>)</literal> terminating the sequence.
    They can appear only at the start of an ARE (after the
    <literal>***:</literal> director if any).
   </para>

   <para>
    In addition to the usual (<firstterm>tight</firstterm>) RE syntax, in which all
    characters are significant, there is an <firstterm>expanded</firstterm> syntax,
    available by specifying the embedded <literal>x</literal> option.
    In the expanded syntax,
    white-space characters in the RE are ignored, as are
    all characters between a <literal>#</literal>
    and the following newline (or the end of the RE).  This
    permits paragraphing and commenting a complex RE.
    There are three exceptions to that basic rule:

    <itemizedlist>
     <listitem>
      <para>
       a white-space character or <literal>#</literal> preceded by <literal>\</literal> is
       retained
      </para>
     </listitem>
     <listitem>
      <para>
       white space or <literal>#</literal> within a bracket expression is retained
      </para>
     </listitem>
     <listitem>
      <para>
       white space and comments cannot appear within multi-character symbols,
       such as <literal>(?:</literal>
      </para>
     </listitem>
    </itemizedlist>

    For this purpose, white-space characters are blank, tab, newline, and
    any character that belongs to the <replaceable>space</replaceable> character class.
   </para>

   <para>
    Finally, in an ARE, outside bracket expressions, the sequence
    <literal>(?#</literal><replaceable>ttt</replaceable><literal>)</literal>